The flame retardancy of polyester or nylon may be obtained by mixing with various additives. Generally, halogenated compounds, especially polybrominated aromatic compounds have been used as the flame retardant additives in these types of polymers. It is commonly believed the additive restrains the free radicals reaction in the gas phase of the flame when the product is lit, which makes halogenated flame retardants widely used as the additives for different types polymer material including polyester and nylon. However, in the last 15 years, halogenated flame retardants have been scrutinized on account of ecological concern. Presently, the flame retardant industry is changing towards development of the environment friendly flame retardant additives under the pressure. Phosphorus product is a logical substitute for halogenated flame retardants. In some applications, the phosphorus retardant shows the same high activity with that of halogenated flame retardants, but the phosphorus retardant is rarely used. Most of the phosphorus-containing retardants provide flame retardant activity by condensed-phase reaction, promotion of the polymer carbonization, and char conversion. The effectiveness of the methods obviously depends on the polymer used in connection with the retardant therein. Therefore, phosphorus-containing structure shall be designed as useful for various polymers. In the late 1970s and early 1980s, various salts of diaryl phosphinic acid, alkyl aryl phosphinic acid, or dialkyl phosphinic acid are prepared, such as the aluminum or zinc salt thereof, as shown in U.S. Pat. Nos. 4,180,495; 4,208,321; and 4,208,322, where the phosphinate is added to PET or polymerizes with polyester at 10-20 wt % and the flame retardancy is improved as shown by measuring the Limiting Oxygen Index (LOI).
The addition reaction of alkyne with P—H containing phosphinic acid compound as initiated by the free radical is known: U.S. Pat. No. 5,647,995A discloses the preparation of a series of alkyl phosphinic acid compounds by the reaction. U.S. Pat. No. 6,727,335B2 discloses the preparation of polymerization phosphinic acid with high polymerization degree by using the reaction, and the polymerization route is as follows:

Obviously, the preparation method provides very limited range for the selection of the polymer end group, which is only suitable for an olefin or alkane having 2 carbon atoms or more or H atoms. The effect of the end group on the performance of the polymer may be ignored when the polymerization degree is high; however, for polymers having low polymerization degree, the effect of the end group on the performance of the polymer is great.